The present invention relates to an exposure apparatus, an exposure method, and a semiconductor device manufacturing method.
The mainstream of conventional exposure apparatuses has been step-and-repeat exposure apparatuses (so-called steppers) in which a wafer stage is positioned on a plane, then exposure processes are repeated for the wafer on the stage. In recent years, however, as semiconductor circuits are refined in structure more and more, there have appeared so-called scanning exposure apparatuses, in each of which a circuit pattern drawn reticle (mask) and a wafer (substrate) are put on their stages, so that they are scanned synchronously and exposed to light. Such scanning exposure apparatuses are now employed positively for mass production processes of wafers. One of the reasons why the stepper is replaced with such a scanning exposure apparatus is that the scanning exposure apparatus can assume a larger exposure field than the stepper. Another reason for the replacement is characteristics specific to the scanning exposure including the easiness to make uniform the contrast in light exposure.
FIG. 10 shows a schematic block diagram of a scanning exposure apparatus. A KrF excimer laser is often used as a light source 10. The beam from the light source 10 is formed in a lighting optical system 11, then irradiated on a substrate (reticle) 13 held on a reticle stage (mask stage) 1 through a slit of about a few millimeters. The beam passing through a projection optical system 14 then reaches to a wafer 16 held on a wafer stage (substrate stage) 2. At this time, the wafer stage 2 and the reticle stage 1 are moved together at a constant speed in the opposite direction, thereby an exposure field wider than the slit is obtained. The reason why those stages 2 and 1 are moved together in the opposite directions is to turn over the subject focused image in the projection optical system 14.
The positions of the reticle stage 1 and the wafer stage 2 in the translation direction are measured precisely with the use of laser measuring machines 17 and 18. The positions of those stages 1 and 2 in the vertical direction are measured as follows; at first, a focusing detection system 3 detects a relative distance between the wafer surface and the exposure imaging surface, and then the wafer stage 2 is driven so as to align the wafer surface to the exposure imaging surface according to the obtained focusing measurement value. The surface of the wafer 15 must be aligned to the exposure imaging surface in the area where the light is irradiated through the slit. Consequently, the wafer stage 2 must be driven in the Z direction (focusing) and the tilting direction (leveling), respectively. This is one of the characteristics of the scanning exposure apparatus, thereby providing an advantage that the above stages 1 and 2 are driven precisely for adjustment of both focusing and leveling on the subject chip.
It is well known that the exposure performance of the scanning exposure apparatus is much affected by a relative position error, that is, a synchronization error in the horizontal direction between the reticle stage 1 and the wafer stage 2 that are synchronously scanned. In addition, the moving average of the synchronization error in the slit corresponds to a deviation of an image to be exposed, that is, a distortion and the moving standard deviation corresponds to an image contrast. Consequently, how to minimize this synchronization error is one of the major technical problems that must be solved for semiconductor manufacturing processes that are getting refined more and more.
On the other hand, driving of the above two stages 1 and 2 for adjustment of both focusing and leveling during scanning exposure is indispensable for the scanning exposure apparatus as described above. However, such driving often causes the synchronization error to become worse. Especially, because the wafer stage 15 is driven for both leveling and driving, the driving is apt to affect the synchronization error as other components, for example, the driving in the xcfx89x direction affects the y direction or the driving in the xcfx89y direction affects the x direction. It is needless to say that in order to avoid such a problem, therefore, a control compensator is designed so as to reduce such an influence on other components with the use of various controlling techniques. In addition, an actual driving distance for adjustment of both focusing and leveling depends significantly on the surface accuracy of the subject wafer to be exposed to light and the flatness of the wafer chuck used to absorb and hold the wafer. It is difficult to solve the problem only with the controlling method.
Especially, it is very difficult to manage the flatness of each wafer so as to suppress the synchronization error to be equal to or under a fixed value even with the use of the same exposure apparatus, since the flatness differs among semiconductor manufacturing processes or production lots.
The productivity of the scanning exposure apparatus can be increased in proportion to an increase of the scanning speed. As a result, a track of stage driving for adjustment of leveling just on a single chip comes to have a high frequency. Generally, the higher the frequency becomes, the lower the follow-up performance becomes in an actuator control system employed for stages. At the same time, the influence of such stage driving on other components becomes large unavoidably. When the scanning speed is increased, therefore, the synchronization accuracy is degraded even when the flatness is the same among wafers.
As described above, the scanning speed affects the synchronization error and this synchronization error affects the exposure performance significantly. However, because the scanning speed is usually set according to such factors as resist sensitivity, exposure amount, etc., the synchronization error has become subordinate in the performance to be decided by other items. Such a method for deciding a scanning speed requires a lot of time for deciding semiconductor manufacturing process conditions and causes the manufacturing yield to drop due to a difference among wafer surface accuracy values.
Under such circumstances, it is an object of the present invention to provide an exposure apparatus, an exposure method, and a semiconductor device manufacturing method enabled to decide an optimal scanning speed according to such manufacturing process conditions as flatness of a substrate, etc., thereby exposing subject wafers to light at a high yield while both exposure performance and productivity are kept at a high level, respectively.
It is another object of the present invention to provide an exposure apparatus, an exposure method, and a semiconductor device manufacturing method that can prevent the processing capability, that is, the throughput of the exposure apparatus from going low, to improve both imaging performance and productivity, and to realize a high yield by deciding an optimal scanning speed for each of a plurality of areas on the subject substrate.
It is another object of the present invention to provide a scan exposure apparatus comprising: a mask stage on which a mask is to be placed; a substrate stage on which a substrate is to be placed; a detection unit for detecting a surface shape of the substrate in each of a plurality of areas thereof, the surface shape being taken into consideration to drive the substrate stage in an exposure process; and a controller for deciding scanning speeds of the mask stage and the substrate stage for each of a plurality of the areas based on the result of a detection by the detection unit so as not to exceed a predetermined value of a synchronization error between the mask stage and the substrate stage.
It is still another object of the present invention to provide the exposure apparatus, wherein the controller includes a track creating device for creating a driving track of the substrate stage, which is used to drive the substrate stage in the exposure process, based on the result of a detection by the detection unit; and an estimating device for estimating a synchronization error between the mask stage and the substrate stage when the substrate is driven along the driving track created by the track creating device; and the controller decides scanning speeds of the mask stage and the substrate stage for each of a plurality of the areas so as not to exceed the predetermined value of the synchronization error estimated by the estimating device.
It is still another object of the present invention to provide the exposure apparatus, wherein the detection unit detects a position of the surface of the substrate in the vertical direction in each of a plurality of the areas.
It is still another object of the present invention to provide the exposure apparatus, wherein the detection unit detects a distance between the surface of the substrate and the focusing surface of a projection optical system for projecting a pattern of the reticle in each of a plurality of the areas.
It is still another object of the present invention to provide the exposure apparatus, wherein each of a plurality of the areas respectively corresponds to one of a plurality of shot areas on the substrate and the controller decides scanning speeds of the mask stage and the substrate stage for each of the areas.
It is still another object of the present invention to provide the exposure apparatus, which further includes a measuring instrument for measuring a synchronization error between the substrate stage and the mask stage when the exposure process is executed; and the controller includes a changing device for changing the scanning speeds of the mask stage and the substrate stage decided for each of a plurality of the areas based on the result of measurement by the measuring instrument.
It is still another object of the present invention to provide the exposure apparatus, wherein the detection unit detects a surface shape of each area on the substrate while both of the mask stage and the substrate stage are driven for scanning.
It is still another object of the present invention to provide the exposure apparatus, wherein a detection by the detection unit is done before an actual exposure operation.
It is still another object of the present invention to provide a controlling method for controlling an exposure apparatus provided with a mask stage on which a mask is to be placed and a substrate stage on which a substrate is to be placed and enabled to expose the substrate to light with use of a pattern of the mask while both of the mask stage and the substrate are synchronously scanned, the method comprising: a detecting process of detecting a surface shape in each of a plurality of areas on the substrate, the surface shape being taken into consideration to drive the substrate stage in an exposure process; and a scanning speed deciding process of deciding scanning speeds of the mask stage and the substrate stage for each of a plurality of the areas based on the result of a detection by the detecting process so as not to exceed a predetermined value of synchronization error between the mask stage and the substrate stage.
It is still another object of the present invention to provide the controlling method, which further includes a track creating process of creating a driving track of the substrate stage, which is used to drive the substrate stage in the exposure process, based on the result of a detection by the detecting process; the scanning speed deciding process includes an estimating process of estimating a synchronization error between the mask stage and the substrate stage when the substrate stage is driven along the driving track created by the track creating process and decides scanning speeds of the mask stage and the substrate stage for each of a plurality of the areas so as not to exceed the predetermined value of the synchronization error estimated by the estimating process.
It is still another object of the present invention to provide the controlling method, wherein the detecting process detects a position of the surface of the substrate in the vertical direction in each of a plurality of the areas.
It is still another object of the present invention to provide the controlling method, wherein the detecting process detects a distance between the surface of the substrate in each of a plurality of the areas and the focusing surface of a projection optical system for projecting a pattern of the reticle.
It is still another object of the present invention to provide the controlling method, wherein each of a plurality of the areas respectively corresponds to one of a plurality of shot areas on the substrate respectively and the scanning speed deciding process decides scanning speeds of the mask stage and the substrate stage for each of a plurality of the shot areas.
It is still another object of the present invention to provide the controlling method, which further includes a measuring process of measuring a synchronization error between the mask stage and the substrate stage when the exposure process is executed; and the scanning speed deciding process includes a changing process of changing the scanning speeds of the mask stage and the substrate stage decided for each of a plurality of the areas based on the result of a measurement by the measuring process.
It is still another object of the present invention to provide the controlling method, wherein the detecting process detects a surface shape of each of a plurality of the areas on the substrate while both of the mask stage and the substrate stage are driven for scanning.
It is still another object of the present invention to provide the controlling method, wherein the detecting process is done before an actual exposure operation.
It is still another object of the present invention to provide a controlling program for controlling an exposure apparatus provided with a mask stage on which a mask is to be placed and a substrate stage on which a substrate is to be placed and enabled to expose the substrate to light with the use of a pattern of the mask while both of the mask stage and the substrate stage are synchronously scanned, the program comprising: a detecting process of detecting a surface shape of each of a plurality of areas on the substrate, the surface shape being taken into consideration to drive the substrate stage in an exposure process; and a scanning speed deciding process of deciding scanning speeds of the mask stage and the substrate stage for each of a plurality of the areas based on the result of a detection by the detecting process so as not to exceed a predetermined value of a synchronization error between the mask stage and the substrate stage.
It is still another object of the present invention to provide an exposure method that uses an exposure method that uses an exposure apparatus provided with a mask stage on which a mask is to be placed and a substrate stage on which a substrate is to be placed and enabled to expose the substrate to light with the use of a pattern of the mask while both of the mask stage and the substrate stage are synchronously scanned, the method comprising: a detecting process of detecting a surface shape of each of a plurality of areas on the substrate; a scanning speed deciding process of deciding scanning speeds of the mask stage and the substrate stage for each of a plurality of the areas based on the result of a detection by the detecting process so as not to exceed a predetermined value of a synchronization error between the mask stage and the substrate stage; and an exposing process of exposing the substrate to light with the use of a pattern of the mask by controlling both of the mask stage and the substrate stage according to the scanning speed decided by the scanning speed deciding process.
It is still another object of the present invention to provide a manufacturing method for manufacturing semiconductor devices, comprising: a process of coating a sensitive material on a substrate; a process of exposing the sensitive material on the substrate to light with the use of the exposure method according to claim 18; and a process of developing the sensitive material after the exposure.
According to the exposure apparatus of the present invention, a scanning speed is decided according to the surface shape of the subject substrate so as not to exceed a predetermined value of a synchronization error (relative positional deviation) between the mask stage and the substrate stage. Consequently, for example, an optimal scanning speed can be selected according to the surface shape of the substrate, which might affect the synchronization error, thereby the maximum productivity is assured while the exposure performance is kept at a high level.
Furthermore, according to the exposure apparatus of the present invention, the scanning speed is decided for each of a plurality of areas on the subject substrate, thereby an optimal scanning speed can be set for each of those areas and the maximum throughput can be obtained corresponding to the predetermined synchronization accuracy and set conditions.